Evaluating the Immunological Properties of Recombinant Hepatitis B Surface Antigen Using a Multitiered <i>In Vivo</i> and <i>In Vitro</i> Approach

The immunological properties of recombinant hepatitis B surface antigen (rHBsAg), prepared using yeast (<i>Saccharomyces cerevisiae</i> [SC]) and Chinese hamster ovary (CHO) cells, were evaluated through <i>in vitro</i> and <i>in vivo</i> assays to support the efficacy of recombinant hepatitis B vaccines. <i>In vitro</i>, antigenicity was assessed by measuring the affinity of rHBsAg to anti-HB antibodies using surface plasmon resonance. <i>In vivo,</i> mice were intraperitoneally injected with 3 µg of simulated vaccines containing anti-HB antibodies absorbed onto aluminum hydroxide adjuvant. Humoral responses were evaluated by measuring serum anti-HB antibody titers and seroconversion rates on days 7, 14, 21, and 28. Cellular immune responses were assessed based on cytokine (Interferon-γ-IFN-γ) and (Tumor Necrosis Factor-α- TNF-α) production from splenic lymphocytes on day 28 postimmunization. A recombinant Huh-7-HBsAg cell line, developed to analyze cellular immune responses, was established through cytotoxicity and apoptosis assays. <i>In vitro</i>, the equilibrium dissociation constant (K_D) of rHBsAg from CHO cells was significantly lower than that from yeast cells, indicating stronger antibody affinity. <i>In vivo</i>, rHBsAg-CHO induced faster and higher antibody titers compared with rHBsAg-SC. Cellular responses showed higher levels of TNF-α and IFN-γ for rHBsAg-CHO. In addition, the rHBsAg-CHO group exhibited higher late apoptosis rates in target cells. The rates induced in the rHBsAg-CHO and rHBsAg-SC groups were 25.0% and 19.2%, respectively. In conclusion, this study demonstrates that the immunological properties of rHBsAg vary based on the expression systems and provides nonclinical data supporting the evaluation of vaccine efficacy.